In the field of vehicular industry the cost of maintenance and service is substantial. The cost due to erroneous equipment, i.e. devices that do not work properly, is very high, e.g. in the airline industry. A defective servo unit can lead to the cancellation of a flight, which may result in huge costs for an airline. Due to these high costs which are generated by defective devices an increasing interest for so called prognostics has developed. Prognostics involves a forecast of future performance and/or condition of a device. There are different measures of performance in the field of prognostics, these prognostic metrics may be, e.g. demonstrated versus design prognostics accuracy, demonstrated versus design prognostics horizon, demonstrated reliability of the prognostic system versus the system it monitors, applicability or robustness of the prognostic technique or system etc. The objective of the prognostics is to forecast when a unit/apparatus/component will break in order to replace the unit without interrupting an operation of a machine/vehicle. The prognostic function is implemented by continuously monitoring data and information about operation and operation conditions, the data is further stored in order to be evaluated. The data is used to predict the remaining useful life of a unit. When the prognostic function determines that the monitored unit is close to its maximum useful life an alarm may sound to an operator or by some other way attract the attention of the operator so that the unit may be replaced immediately or preferably at the next service opportunity.
The problem with this type of prognostics is that the amount of data of operation and operational conditions always has to be updated in relation to replacement/repair of the unit. The problem as such is that the data and the exchangeable units must be kept together in order for the prognostic function to work satisfactorily. For instance, a servo unit may contain ten O-rings. If, during a service check-up, five of these need to be replaced the operating time for the exchanged O-rings is set to 0, but for the remaining O-rings that have not been exchanged the operating time should be kept as it was before the service. Now, when the servo unit is sent back to the vehicle the updated data needs to be sent with the unit, e.g. stored on a separate disc, sent electronically to a control centre of the vehicle or the like, and downloaded into the electric system of the vehicle separately. This type of handling of data is time consuming and there is a risk that the unit and data gets separated wherein wrong data is fed into the system of the vehicle.
It is very hard to predict exactly how a servo unit will behave over a long period of time. It is therefore a desire to collect data from units that have broken down or serviced in order to understand how these units are degrading. This understanding can be used to enhance the prognostic function. The problem with this collection is that this requires data of a defective unit to be sent along with the unit. As mentioned before, there exists a risk that when the data and the unit are sent to a service park the data and the unit gets separated. Experience says that it is very hard for suppliers to get proper feedback of operational data from the technicians.
A further problem with gathering prognostics is that certain individual apparatuses sometimes have intermittently occurring errors which implies that when an apparatus has been dismounted from a vehicle due to e.g. that a test has indicated that an error has occurred in the apparatus, the error may not occur in tests when the apparatus has been dismounted from the vehicle. The result of this may be that the apparatus is sent back and forth between vehicle user and the supplier of the apparatuses, or repair shop, a numerous of times before the supplier can identify the error, which generates high costs for both the supplier as well as the user of the apparatus.
Document U.S. Pat. No. 6,343,252 discloses a system for collecting and analyzing data regarding the operation of gas turbines. The system includes a number of sensors monitoring the gas turbine and outputting operational data to a local computer. A remote database server periodically collects data from several on site systems for a plurality of gas turbines that can be used in a prognostic function. However, this system does not deal with or solves the problems stated above, i.e. that occurs when a part of the gas turbine or the whole turbine itself is dismounted and shipped of for service or repair.
Document WO, A1, 2004/061780 discloses another example of prior art in the field of prognostics. The disclosed system comprises a life indicator of a component of a machine. The life indicator comprises sensors configured to sense a property associated with the machine. The life indicator includes a memory element having a first data structure that determines a damage factor for the component of the machine based data from the sensors. When parts are repaired or replaced the information in the memory element may be reset to reflect the repaired or new state of the component. However, the memory element is maintained in the local interface 212 of the system and hence does not deal with the problems stated above. When, for example, a transmission part is dismounted and sent away for repair the stored data in the memory and the transmission part is separated.
The objective of the invention is to provide a system for prognostics wherein the data about the different components are as reliable as possible and the handling of the exchangeable units is simplified. This results in that the prognostics concerning the different components in an exchangeable unit are as accurate as possible.